A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM), such as carbon fiber paper, which facilitates a delivery of reactants such as hydrogen to the anode and oxygen, typically from air, to the cathode. In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
The electrolyte membrane is typically formed from a layer of ionomer. A typical ionomer is a perfluorosulfonic acid (PFSA) polymer, such as Nafion®, commercially available from the E. I. du Pont de Nemours and Company. The electrodes of the fuel cell are generally formed from a finely divided catalyst. The catalyst may be any electro-catalyst which catalytically supports at least one of an oxidation of hydrogen and a reduction of oxygen for the fuel cell electrochemical reaction. The catalyst is typically a precious metal such as platinum or another platinum-group metal. The catalyst is generally disposed on a carbon support, such as carbon black particles, and is dispersed in an ionomer.
The electrolyte membrane, electrodes, and DM are disposed between a pair of fuel cell plates and sealed, for example, with a gasket providing a substantially fluid-tight seal. The electrolyte membrane also typically has a barrier film or subgasket coupled thereto to provide internal reinforcement and to separate the hydrogen gas and the air supplied to the fuel cell stack. The subgasket generally overlays an edge of the electrolyte membrane and is formed in a secondary operation by cutting a piece of polymeric sheet material and bonding the sheet material to the electrolyte membrane with at least one of compression and an adhesive. Typical subgaskets and means for coupling subgaskets to the electrolyte membrane are described in Assignee's copending U.S. application Ser. No. 11/972,211, the entirety of which is hereby incorporated herein by reference. However, ensuring proper alignment of the polymeric sheet material forming the subgasket with the electrolyte membrane is known to be difficult. Excess polymeric sheet material formed during formation of the subgasket also cannot be reused, resulting in an undesirable waste of material. The overlaying of the subgasket at the edge of the electrolyte membrane can further create an undesirable stress riser within the fuel cell stack.
There is a continuing need for a subgasket and a method for fabricating a subgasket that minimizes production waste, is cost-effective, and facilitates an alignment of the electrolyte membrane and subgasket within the fuel cell. Desirably, the subgasket is mechanically stable and militates against a formation of stress risers within the fuel cell at the junction between the subgasket and the electrolyte membrane.